The invention relates to a process for the trifluoro(or chlorodifluoro or dichlorofluoro)methylation of electrophilic substrates void of electrochemical activity. In particular, the invention relates to the preparation of organic trihalo; i.e., trifluoro(or chlorodifluoro or dicholorofluoro)methyl derivatives, which can be used particularly as synthesis intermediates.
Several processes for introducing a trifluoromethyl group are already known, but, in general, these processes rely on materials which are not readily accessible and/or must be carried out in the presence of catalysts and/or chemical reducing agents. Thus, for example, the trifluoromethylation reaction may be carried out by a radical route from CF.sub.3 I by initiating the reaction by raising the temperature or by irradiation with UV rays (J. Chem. Soc., 1953, p. 1199; U.S. Pat. Nos. 3,016,406 and 3,016,407). However, this method has not yet been applied industrially because access to trifluoromethyl iodide from trifluoroacetyl fluoride according to the scheme: ##STR1## is difficult and costly.
Complex compounds such as ##STR2## (Umemoto et al., Toyo Soda Kenkyu Hokoku 1983, 27(2), 69-73 and C.A. 100: 67911 z) or CH.sub.3 Si--N.dbd.N--CF.sub.3 (Hartkopf et al., Angew. Chem. 1982, 94(6), 444 or C.A. 97: 127170 p) have also been proposed as trifluoromethylation agents.
The trifluoromethylation of olefins has also been performed by means of an electrochemical oxidation of the trifluoroacetate anion using a radical mechanism, as described by Brookes et al. (J. Chem. Soc. Chem. Commun. 1974, 323) and Renaud et al. (Can. J. Chem. 53, 1975, 529).
The trifluoromethylation reaction can also be carried out using CF.sub.3 I or CF.sub.3 Br in the presence of reducing agents and/or activators. Thus, Ishikawa (Chemistry Letters 1984, 517-520) uses zinc-based reducing agents and catalysts based on salts of nickel or of palladium which are complexed with phosphines. The use of zinc, which gives rise to polluted effluents, makes this method unattractive on an industrial scale.